Females find cocaine more addictive than males do

In drug addiction
research, it is well established that an enhanced response to novelty can
predispose certain individuals to addiction.

Research has
previously shown that rats, selectively bred to have an increased locomotor
response to novelty, display differences in the amount of cocaine they self-administer,
compared to rats bred to be less reactive. Not only do they ingest greater
doses of the drug, they also exhibit enhanced impulsivity due to lowered
behavioural inhibition.

An additional
factor that also puts individuals at increased risk for drug abuse is gender. Trend
analysis shows that, compared to men, women begin using cocaine at younger ages,
become addicted to it more quickly and also suffer more intense cravings during
periods of abstinence. A hormonal
element to addiction has also been implicated by women
reporting greater pleasure from smoking cocaine when their estradiol levels are
elevated.

In support of
this, researchers at the University of Michigan found that female rats, selectively
bred to have higher reactivity to novelty, increase self-administration of
cocaine more quickly than male rats also bred to have a heightened response
level. In light of these findings, Jennifer Cummings and colleagues then
investigated whether increased motivation was behind the difference in
behaviour and have sought
to determine the impact of sex on the motivation to
self-administer cocaine.

The study,
published today in Biology
of Sex Differences, revealed an underlying sex
difference in the desire to ingest the drug, regardless of phenotype, with
females showing a greater motivation than males. Interestingly, the researchers
found that male rats, bred to have
a low reactivity to novelty, did not work hard for their dose of cocaine, but
the equivalent female rats did.

The authors explain
“This suggests that whilst this selective breeding has proved “protective” to a
certain degree by reducing the motivation for cocaine, this protection is
limited in females, and ultimately sex overrides behavioural phenotype in this
situation.”